Rectification of alternating currents



July 5, 1932. H. P. HOLLNAGEL ETAL RECTIFICATLON 0F ALTEKRATING GURRENTS Filed Jan. 29.' 1927 2 She ets-Sheet 2 Fig.7.

/o" 5 Inventor-s:

Q Herbert FJ-iollna e|.-

J Gunner A.F.\X/Lnck er.

Their- Attorney.

Patented July 5, 1932 UNITED STATES PATENT OFFICE HERBERT I. HOLLNAGEL, OF SWAMPSCOTT, AND GUNNAR A. I. wmcxnm, OF WORCES- TIER, MASSACHUSETTS, ASSIGNORS TO GENERAL ELEGTBIC COMPANY, A CORPORA- TION OF NEW YORK BEOTHICATION OF ALTEBNATING GUBBENTS Application filed January 29, 1927. Serial No. 184,642.

Our invention relates to the rectification of alternating current, and has for its principal object theprovision of an 1mproved rectifier of the type which comprises a plu- 6 rality of conductive members slightly spaced apart by any suitable means, such as a thin film or spacer of insulating material consistin of a metal oxide or the like. A further ob ect is the provision of an improved system and method of operation whereby a storage battery may be readily charged and maintained in a charged condition by current supplied from the usual house lighting circuit. a

Various types of apparatus have been utilized in the past to rectify the current transmitted between direct and alternating current circuits. Some of these apparatus comprise sheets or disks of difierentmetals spaced apart by a very thin film of insulating material formed between them by sub ect1ng them to an alternating voltage while they are pressed tightly together. These apparatus, as constructed and operated in the past, have not been altogether satisfactory because of the shortness of their useful hfe andbecause of the high pressure which must be maintained between the difierent elements both during the formation of the film and during the operation of the rectifier. In accordance with our invention, these difficulties are minimized or obviated by the provision of a rectifier wherein a very thin spacer of insulating material is interposed between members made respectively of tellurium and of another metal such as magnesium aluminum, zirconium, cerium, thorium, calcium, or the like, which has a readily formed and stable oxide. 4

Our invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Figs. 1 to illustrate various details of a rectifier constructed in accordance with our invention; Figs. 6 and 7 illustrate systems wherein this rectifier is utilized to transmit current between an alternating current circuit and a direct current translating device shown as a storage battery; and Fig. 8 shows a modified embodiment ofthe rectifier.

Fig. 1 illustrates a rectifier comprising a plurality of elements 1 made of tellurium, or of tellurium combined with small amounts of selenium, copper, and sodium, which may be cast or otherwise inserted between a plurality of elements each made of a magnesium sheet 2 welded or otherwise brought into electrical contact with a copper sheet 3. lit will be observed that the copper sheets at either end of the rectifier are provided with end terminals 4 and 5 and with intermediate terminals 4a, 5a and s; and that the terminal 6% is attached to or forms a part out a copper sheet which is inserted between the two halves of the rectifier. lhe manner in which the rectifier is connected between an alternating current supply circuit and a direct current load circuit will be explained in connection with Figs. 6 and 7.

The various elements of the rectifier are supported within a band 6 which is illustrated as made of insulation, but under certain conditions of operation may be made of a conductive material such as copper. An insulation member 7 preferably made of a compound comprising asbestos and pitch is cast or otherwise interposed between the edges of the difl'erent elements and the inner surface of the band 6.'

Figs. 2 to 5 illustrate various steps in the manufacture of the rectifier. As lndicated by Fig. 2, a member 8 slotted at 9 to receive the elements 23 is supported on a base 10 and is arranged at its lower edge to fit tightly against the inner sides of the band 6 as shown more clearly by Fig. 3.

Fig. 3 shows the elements 2-3-as arranged ,in the slots 9 to permit the casting of the insulation members 7 between the edges of these elements and the inner surfaces of the band 6. It will of course be understood that the opposite edges of the elements 23 are encased in the insulation members 7 and are thus fixed tothe band 6.

Fig. 4 illustrates the rectifier as it appears prior to the casting of the tellurium elements 1 between the bimetallic elements 2-3.

Fig. 5 shows a member 11 which is slotted to receive the lower end or ends of the elements 2-3 and to fit within the band 6 to permit casting of the tellurium elements, these elements being made somewhat shorter than the elements 2--3 to facilitatecooling of the rectifier.

While the tellurium elements ,1 have been described as cast by pouring molten tellurium between the magnesium-copper elements 2-3, it should be understood that they may 'be die cast or may be in the form of tellurium sheets or disks clamped between bimetallic elements 23 as illustrated by Fig. 8.

Fig. 8 shows a rectifierv which comprises a plurality of disk-shaped elements mounted on a bolt 12 and insulated therefrom by an insulation sleeve 13 and an insulation washer 14. In this modification of the invention, contact between the different elements is maintained by nuts 15 and 16. End terminals l7 and 18 and a plurality of intermediate terminals 17a, 18a and 19a are provided for connecting the rectifier between the alternating current supply and the direct current load circuits in a manner to permit rectification of both halves of the alternating current wave.

It is essential for proper operation of the rectifier that the tellurium and magnesium be spaced apart slightly. This may be accomplished by any suitable spacer inserted between the tellurium and magnesium. One way of accomplishing this result is the formation of a very thin insulating film between these elements. Such a film may be produced by different processes. If the tellurium is cast between the composite magnesium-copper elements as described in connection with Figs. 1 to 5, an insulation film of oxide or the like may be formed on the magnesium between the tellurium and magnesium during the process of casting. In the case of the rectifier illustrated by Fig. 8, the insulating spacer may be formed in the usual manner by subjecting the rectifier to an alternating voltage or in any other suitable manner.

In the construction of rectifiers having elements of tellurium cast or clamped between magnesium-copper elements, it has been found desirable, although not absolutely essential, to mix about seven parts of copper and one-half of one part of sodium to one hundred parts of tellurium. The effect of the copper is to reduce the resistance of the tellurium element and decrease the tendency of the rectifier to heat. The effect of the sodium is not well understood but it seems to facilitate the formation of the insulating film or spacer between the tellurium and magnesium.

The current at which the operation of the rectifier becomes stable is dependent on the conditions to which the rectifier is subjected.

A condenser connected in shunt to the recti fier has been found useful in stabilizing the operation of the rectifier and prolonging its useful life. The stable operating current of the rectifier ismaterially increased in value if some means are provided for regulating the rectifier voltage in response to change in the rectified current. This effect may be produced either by means of a resistor connected to the alternating current supply transformer in series with the rectifier or by using a supply transformer with loosely coup-led primary and secondary windings. For example, in the case of a rectifier having an impressed voltage of about thirteen volts and a current output of from .3 to .4 amperes, satisfactory results have been secured by using a regulating resistor of thirty ohms. The size of the resistor required for good regulation will of course be dependent on the size of the rectifier and the voltage at which it is operated.

Fig. 6 shows a rectifying system which comprises an alternating current supply transformer 19, a capacitor 20, and a rectifier provided with terminals 21 and 22 connected to the secondary circuit of the transformer 19 and with terminals 23, 24c and 25 connected to a load shown as a battery 26. It will be apparent that the terminals 23 and 25 have the same potential and may be a copper or other conductive bond within which the rectifier is supported.

Assuming the upper secondary terminal of the transformer to be positive, rectified current is supplied from the transformer to the battery as indicated by the full line arrows. When the lower secondary terminal is positive, current is transmitted between the trans former and battery as indicated by the arrows shown in broken lines.

Fig. 7 shows a system which differs from that of Fig. 6 in that two rectifier units are connected to the battery in parallel and in that a voltage regulating resistor is connected in one of the secondary leads of the transformer. It will be apparent that the potential drop of the resistor 27 will vary directly as the current supplied to the battery through the rectifier. Under these conditions any increase in the rectified current tends to lower the voltage applied to the rectifier and any decrease in this current tends to raise the voltage applied to the rectifier. The regulation of the rectifier voltage in this manner has been found to greatly increase the value of current at which operation of the rectifier becomes stable.

The embodiments of the invention illustrated and described herein have been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the different conditions encountered in its use and we therefore aim to cover by the appended claims all modifications within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination of a member containing'tellurium, a bimetallic element comprising members consisting respectively of COP. er and magnesium, and aninsulation spacer mterpos'ed between said tellurium and magnesium members, said insulation spacer constituting an asymmetric current conducting film at the junction of said tellurium and magnesium members. 2. The combination of a member containing a mixture of tellurium and sodium, an element consisting of magnesium, and a spacer interposed between saidmember and said element, said spacer constituting an asymmetric current conducting film at the junction of said element consisting of magnesium and of said member containing said mixture.

3. The combination of a member contain-, ing a mixture of tellurium, copper and so dium, an element consisting of magnesium, and a spacer interposed between said member and said element, said spacer constituting an asymmetric current conducting film at the junction of said element consisting of magnesium and of said member containing said mixture.

4. The combination of a member containing a mixture of tellurium, copper and sodium, a bimetallic member comprising elements consisting respectively of copper and magnesium, anda spacer interposed between the magnesium surface of said bimetallic member and a surface of the other of said 0 members, said spacer constituting an asym-' metric current conducting film at the junction of said surfaces.

In witness whereof, we have hereunto set our hands this 27th day-of'January 1927. HERBERT P. @HOLLNAGEL. GUNNAR A. F. WINCKLER. 

